(1) Field of the Invention
The present invention relates to a magnetic head for a magneto-optical recording device employing a magnetic field modulating type recording system.
(2) Description of Related Art
In a known magneto-optical recording device employing a magnetic field modulating type recording system, information is recorded onto a magnetic recording medium by a magnetic head under the condition where the magnetic recording medium is partially heated by irradiation of a laser beam to thereby reduce a coercive force. According to such a magneto-optical recording device, vertical magnetic recording can be carried out by a relatively small magnetic field.
Referring to FIG. 12A which is a schematic illustration of the magneto-optical recording device in the prior art, reference numeral 1 designates a magnetic recording medium. The magnetic recording medium 1 is constructed of a substrate 2 (e.g., polycarbonate) having a light transmissivity, a vertical magnetization film 3 (e.g., TbFeCo) formed on an upper surface of the substrate 2, and a protection film 4 (e.g., Si.sub.3 N.sub.4) formed on an upper surface of the vertical magnetization film 3. A condenser lens 5 is located below the magnetic recording medium 1 to condense a laser beam L and irradiate the same upon the vertical magnetization film 3, so that an irradiated portion of the vertical magnetization film 3 is heated by the laser beam L.
A magnetic head 6 is located above the magnetic recording medium 1 to carry out vertical magnetic recording to the heated portion of the vertical magnetization film 3. The magnetic head 6 is constructed of a rod-like main pole 7 and a coil 8 wound around the main pole 7. When a recording current is supplied to the coil 8, a magnetic flux .phi. is generated from the magnetic head 6, thereby generating a magnetic field. As a result, the vertical magnetization film 3 is vertically magnetized by this magnetic field to thereby carry out the vertical recording.
In the magneto-optical recording device utilizing the above-mentioned principle, it is theoretically preferable that the intensity of the recording magnetic field due to the magnetic flux to be generated from a lower end of the main pole 7 becomes maximum near the vertical magnetization film 3.
However, it is necessary to define a spacing between the main pole 7 and the magnetic recording medium 1 since a hardness and a bond strength of the film surface of the magnetic recording medium 1 are small.
Moreover, since the substrate 2 of the magnetic recording medium 1 is normally formed of a soft material such as a synthetic resin, a rigidity of the substrate 2 is low, and a flatness of the substrate 2 is limited. Accordingly, surface vibration of the magnetic recording medium 1 during rotation thereof cannot be avoided. Therefore, the spacing between the main pole 7 and the magnetic recording medium 1 must be made large.
Further, because of the presence of this spacing and the flat shape of the end surface of the main pole 7, it is necessary to form a large magnetic field in order to realize predetermined vertical magnetization. Thus, it is impossible to sufficiently make use of the aforementioned advantage of the magneto-optical recording device such that information can be recorded by a small magnetic field.
To solve the above problem, the present applicant proposed a magnetic head 100 as shown in FIG. 12B. The magnetic head 100 is constructed of a main pole 7, a pair of return path cores 9 disposed on opposite sides (front and rear sides) of the main pole 7 in such a manner that each return path core 9 connects opposite end portions of the main pole 7, and a pair of gaps 10 interposed between the main pole 7 and the two return path cores 9, respectively. Each gap 10 is formed of a non-magnetic insulating material such as glass and CaTiO.sub.3.
In the magnetic head 100, two magnetic paths passing through the two return path cores 9 are formed by the return path cores 9 disposed on the opposite sides of the main pole 7, thereby increasing a magnetic flux density at the end portion of the main pole 7 in the vicinity of the magnetic recording medium 1 to widely generate a uniform magnetic field to be applied to the magnetic recording medium 1.
The construction of the magnetic head 100 having the two return path cores 9 on the opposite sides of the main pole 7 as shown in FIG. 12B is an example in the prior art. As another example like the above construction, it is known that a magnetic head is constructed of a main pole 7, a single return path core 9 disposed on one side of the main pole 7, and a single gap 10 interposed between the main pole 7 and the return path core 9.
In this construction of the magnetic head having the single return path core 9, the same operation as in the magnetic head having the two return path cores 9 is obtained with the exception that a range of application of the magnetic field is smaller than that in the magnetic head having the two return path cores 9.
Although not especially shown, each of the magnetic heads shown in FIGS. 12A and 12B is fixed to a slider for defining a given spacing between the magnetic head and the magnetic recording medium 1.
As mentioned above, the magnetic head 100 is provided with the two gaps 10 formed of a non-magnetic insulating material, each being interposed between the main pole 7 and the return path core 9. However, as a leakage magnetic field Hg leaking from the main pole 7 to each gap 10 is large, a large magnetomotive force is required so as to enlarge a magnetic field to be generated from the core end.
In a magnetic head for audio equipments, a spacer formed of a non-magnetic conductive material such as Cu and Ti is inserted in each gap 10 to generate an eddy current and accordingly generate a magnetic field He due to the eddy current so as to suppress the leakage magnetic field Hg to each gap 10 and relatively enlarge the magnetic field to be generated from the core end.
That is, the eddy current is generated in such a direction as to suppress the leakage magnetic field Hg. In other words, the eddy current is generated in such a direction as to generate the magnetic field He directed counter to the leakage magnetic field Hg. As a result, while an eddy current loss is generated, the magnetic field He due to the eddy current is synthesized with the magnetic field generated from the core end to thereby increase the intensity of the total magnetic field to be generated from the magnetic head.
However, in the case that this method is applied to a magnetic field modulating type magnetic head, there is a problem such that since a cross sectional area in each gap 10 is small as compared with that in the magnetic head for audio equipments, the effect of suppressing the leakage magnetic field Hg, that is, a "skin effect" indicating a degree of penetration of a high-frequency electromagnetic wave upon incidence thereof on the spacer becomes relatively small. As a result, it is difficult to increase the total magentic field to be generated from the magnetic head by synthesizing the magnetic field He due to the eddy current with the magnetic field generated from the core end.
Further, as the magnetic field He due to the eddy current is locally generated, a distribution of the magnetic field at the core end cannot be generally improved. Therefore, it has been demanded to effectively improve the distribution of the magnetic field at the core end.